Electrolytic refining of tin.



ioniriii ELMER SPERRY, OF BROOKLYN, NEW YORK.

ELECTROLYTIC REFINING OF TIN.

Specification of Letters Patent.

Patented Dec. 24, 1907.

Application filed September 15,1906. Serial No. 334.754.

To all whom it may concern:

Be it known that I, ELMER A. SPERRY, a citizen ofthe United States, residing at Brooklyn, in the county of ueens and State of New York, have invents new and useful Improvements in Electrolytic Refining of Tin, of which the following is a specification.

This invention relates to the refining of tin, such as sla tin, dross tin or other impure tins or alloys of tin, or tin bearingmaterial.

I have discovered there are conditions under which an electric deposit of tin of great purity may be produced. i Tin is a peculiar metal in that it alloys with a reat many other metals and when so al oyed, even though the foreign metal may be present in minute quantity, the luster of the tin is do stroyed, or so far reduced as to render it undesirable. In connection with the electrical production of tin of great purity I have discovered that at least two elements are essential: the first that the electrolyte used in the depositing bath should not only be suited to the conditions of the de osition, but the tin bearing materialshould itself have received a previous treatmentjwith reference to its electrical depositing characteristic or the characteristics of the electrolytic deposition of its tin content, and it is .to the satisfying of these conditions together'wi'th other collateral details that the presentinvention relates.

The first step in the present method or process is thetreating or conditioning the tin bearing material {this may consist in eliminating some of the impurities which are found to prevent a deposit of high purity. Again I have found that some of the impurities upon or within the cathode tin are due to particles or bodies of slime emanating from the anode and being brought in contact with the oathode, and it is one of the objects of this invention to .overcome this difficulty, I find that there are a number of electrolytes that may be employed with advantage,

some have advantage over others when handlinganodes bearing certain impurities;

among these may be cited the sulfates, ammonium-oxalate, ammonium-sulfid, the chlorids and i'luorids, hydrochloric and hydroiiuoric acids; all of these I assume have heretofore been known in- -the art; The novelty in the present invention rests in the combined steps of the process, which together produce the result or such a portion of such steps as produce the result, as is ointed out in the claims hereto annexed an forming a part hereof. .I prefer an electrolyte in which copper is not soluble under the working conditions. I find that in most electrolytes the objectionable impurities, among which is lead, are segregated out from the other impurities which are left behind and together with the lead tend to deposit upon the cathode along with the tin, especial y is this true at-an elevated tem erature which is preferable in increasing tfie electrical conductivity of the electrolytes and aiding in holding the cost of operation within commercial limits.

From one standpoint it may be'understood that this cost should be as low as ossible, especially from the fact that the sac eslimes and impurities in the raw tin or tin bearin material carry but comparatively small va ues. A particular difiiculty with im ure tin deposit at the cathode, and especial y when the impurity is lead or associated with lead, consists in fact that such cathodes are spongy and porous and unfit for meltin because" of excessive amounts of dross, whidli is formed.

I first melt the anode tin, alloy, or tin hearing material and whilestill in the molten state and while considerably above the fusing point I prefer to treat it by a recess known as oling; this is accomplis ed by plunging a 0g or logs of green wood into the molten mass whereupon the steam gradually generated from the water and salts in the sap of the wood agitates the metal and causes it together with the impurities to be subjected to the combined action of the gases and vapors and the air whereby some of the impurities become oxidized and eliminated. The dross is allowed to accumulate on the top the metal, which consists in certain ox1dation products of the lead and also some of the other objectionable impurities; this may be skimmed off and removed, leaving the tin bearing material sufliciently free or low in these impurities so that it may be em loyed to yield a cathode product of the esired purity when electrolyzed in a suitable elec' trolyte. During the cling operation or in lieu thereof I may emplby a foreign substance as an oxidating agent, such for instance as a nitrating element. For instance I may employ saltpeter which is introduced very gradually into the molten mass to hasten the formation of the oxidation products. The use of the nitrating element only becomes necessary when the objectionable impurities are present in certain complex combinations, or in excessive amounts. It is while the tin bearing material is at high temperature that in some instances 1 find it of advantage to add a sliming or non-soluble element, preferably a metallic element for the purpose hereinafter stated. The melt is now allowed to stand for some time, quiescent for the pur pose of cooling, as one of the important features for best results is that the temperature should be correct when the anodes are cast. I have found that far better anodes are made from the tin bearing material, or alloys, that are cast cool than when poured hot. Anodes poured at a low temperature that is not far removed from its congealing point and especially at the predetermined temperature dissolve more smoothly and act far more uniformly, being freer from crystalline structure and irregularities and are also hi her in electrical conductivity, all of which wi l he recognized as being important in this art. This casting melt may not be the same as the treating melt, but may be a separate melt and in different form of furnace and fixtures or it may be of advantage to treat the alloy at one point and to electrolyze it at a distant point. The anodes are now ready for the final step, namely, electro depositing; this is accomplished in the usual manner and in a general way--similarto copper de osition. In the case of tin great care is here necessary to prevent the anode slim'es from reaching the cathodes, inasmuch as the amount of these slimes are considerably in excess of the amount present in the case of copper. Any of the well known methods may be employed for this process, as for instance, the use of a suitable diaphragm located betweenthe electrodes or surrounding one of such electrodes. Furthermore, 1 prefer in most instances to circulate the electrolyte or anolyte to facilitate the removal of the impurities and .slimes and to prevent them from accumulating in the immediate neighborhood of the anodes and thus cut down the electric conductivity of the bath. This circulation I may also utilize for maintenance of proper temperature and also for distributing such temperature throughout the cell or group of cells. For best results the temperature should be held with some electrolytes as high as 85 degrees centigrade; usually some degrees lower is a fair avera e found ractical to maintain. In cases W ere the impurities are not found to produce slimes but tend to dissolve or dis seminate throughout the electrolyte it is found an advantage to cmploy a coagulating material which is suitably added to the bath or to the molten tin'bearing material or alloy as mentioned above. This naturally adds to bind or mass the impurities as they are released at the anode: to illustrate such metal copper may be mentioned a small amount of whichis dissolved and distributed llii'ollg'll out the melt.

given as illustrating one method of carrying The refined tin produced by this method is of a high degree of purity; the total impurity should be well under 01% it is farther char- :iclcrized by a high degree of brightness and a remarkable freedom from tarnishing on exposurc to damp atmosphere; the durability a nd tenacity with which it retains its silvery luster is one of its marked characteristics.

The impurities accumulate in the electrolyte and are eliminated by periodical withdrawal of portions and treatment thereof or withdrawal and replacing with pure and fresh electrolyte. The treatment in this case maybe illustrated in the use of stanuous chlorid as electrolyte. Here the electrolyte withdrawn is treated with quick lime or milk of lime or a suitable alkali and the tin precipitated as tin oXyhydrate, which is utilized as raw tin oXid, is smelted or is roasted and separated or concentrated to eliminate the impurities. The tin may then either be smelted or utilized as fixed oXid; the impurities in Whole or part are left behind in the precipitating process. That portion thrown down with. the precipitate is eliminated in the roasting or concentrating or separating process.

Having pointed out the essential features of my process or method of refining tin, I may state that the process should in no way be limited to the exact details of the method described in reference to any particular step or the exact order of steps which are simply my process into eflect. It should also be mentioned that my process may be varied in some of its parts to suit the special alloy or peculiarities of raw tin or alloy to be refined; thus suiting itself to the. characteristics of the impurity carried. In these cases, some of the steps may be altered or omitted entirely and the invention extends to such use as set forth in the claims forming a part hereof.

1 claim,

.1. Themethod of refining tin which con sists in dissolving a tin bearing material in a suitable electrolyte passing an electric current through an electrolytic diaphragm within the electrolyte, and depositing tin at the cathode.

2. The method of refining tin which consists in electrolytically dissolving tin bearing material at the anode in the suitable electrolyte and depositing tin at the cathode, and suitably isolating the cathode from contact with the residues of such solution.

3. The method of refining tin which consists in dissolving a tin bearing material in a suitable electrolyte passing an electric current through an electrolytic diaphragm within lhc electrolyte depositing tin at the cathode and circulating the electrolyte.

4. The method of refining tin which consists in dissolving a tin bearing material in a were? suitable compound electrolyte passing an elect *ic current through an electrolytic dic phlegm Within the electrolyte depositing tin at the cathode and circulating the acolyte.

5. The method of refining tin which consists in melting the raw alloy, bringing the molten material to ahigh temperature, thus i changing its elect-r0 depositing characteristics and electro depositing the mess so treated in a suitable electrolyte.

6. The method of refining tin which con-- sists in bringing the material While in the molten state to a high. temperature, thus bringing about a condition which will yield at redeterinined characteristic in the electrol Fytic deposit of the tin content and electrolyzing the resulting mass in a suitable electrolyte and depositing tin tl'ierelrom.

7. The method of refining tin whic 1 consists in bringing the material while in the molten state to at high temgerziturc, thus bringing about a condition which will .ld a predetermined characteristic in the electrolytic deposit of the tin content iuid elcctrolyzing the resulling mass and depositing Lin 1 therefrom. in the presence ol e halogen acid.

8. The method of refining tin which consists in'i'noltii'ig the raw alloy, bringing the molten material to Qhlllgll temperature, thus changing its electz'o depositing characteristic and electro depositi o the moss so treated in it suitable electrolyte, at an elevated team 1 perature.

5. The method oi refining tin, which consists in melting the alloy or tin hearing me,- teriel treating the molten material to improve its slime coagulating qualities and electro depositing the resulting moss in it suitable electrolyte 1C- Tl'ic inci oil oi rcliningr tin, which consist-s. in melting the alley or tin hearing meteriul, treating tlf, molten umterial to iinprove its slime coagulating 'oiiolitics and. also i to a high temperature to change its clccl'ro 5 dc itiug cl zcterigic and electro depositthe resulting mess in osuimhlc' cloct ol ilie u'icthoil of refining tin, which consists in melting sists of melting the row alloy, hringing the molten mature to a. high temperature, thus tics, cooling Qhe HESS to a predetermined 7 point, pouring i: i molds,- and electro (lepositing the mess thus obtained in suiteole electrolyte.

15. The method of rei'ining tic, which co11- sisls in suitably oreoaring anodes of tin hearing mater el disso v' 3 some in suitable electrolyte sing electric current through an electrolytic diaphragm within the electrolyte, depositing tin at the cathode, circu-' lilting the ele v olyte, withdrawing portion of such electrolyte and treating some to eliminate impurities.

16" The on hod of refining tin which consi' in so i w preparing enooes tin laceriug materiel, oissoiving some in a suitable electrolyte, passing electric current through an electrolytic dio ihragin wi te trolytc, dopositi tin at the cathode 3 letting the clcc i1I(Ji yUJ, withdrawing a po of such electrolyte and treating some to eliminate lioth the tin content and impure tics and returning the tin to the process,

1'7. The moth-u oi refining tin Winch con ello r, suitably slots in me no the v on or treeti 11g the molten mass at an elevated tour peritture to ini 'irove slimecoegu ating "is. allowing the mess to cool to e "eredeterin ed gioint, the

the 1. cell,

-1 n 0 Jl m: iii Slacii such electro l yte precipilz Joel: mo teriels from such portions, the precipitate v '9' u ',;i l suitzmly ceucentictni it to eliminate purities mid returning tie no d precipi to the process. 

